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| Ok, now what are the differences between a Keithley 195 and a 195A? |
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| alm:
--- Quote from: wkb on September 22, 2022, 06:32:11 am ---As for the AC & current specs: as far as I can tell the Option 1950 is the same one used for the 195 and 195A? So this puzzles me a bit. --- End quote --- There's a couple of options here. Maybe there was a change to the later production options, but that they didn't change the model. Or maybe the change is in the main unit, for example a firmware change. Or it could be that there was no change at all, and the improved spec is the result of having more data available on the stability of the units, like HP did with the 3456A. But in the case of HP we know this because they described it in HP Journal. I'm not aware of such a resource for Keithley, so we have to assume the lower accuracy for the 195. |
| wkb:
--- Quote from: alm on September 22, 2022, 08:27:04 am --- --- Quote from: wkb on September 22, 2022, 06:32:11 am ---As for the AC & current specs: as far as I can tell the Option 1950 is the same one used for the 195 and 195A? So this puzzles me a bit. --- End quote --- There's a couple of options here. Maybe there was a change to the later production options, but that they didn't change the model. Or maybe the change is in the main unit, for example a firmware change. Or it could be that there was no change at all, and the improved spec is the result of having more data available on the stability of the units, like HP did with the 3456A. But in the case of HP we know this because they described it in HP Journal. I'm not aware of such a resource for Keithley, so we have to assume the lower accuracy for the 195. --- End quote --- Well, yes, all possible. Beter stability components maybe. First I need to get the Uncal error out of the way, only once done I will investigate the OSHW Option 1950 board. thanks! |
| wkb:
--- Quote from: Swainster on September 22, 2022, 04:17:58 am ---I've got a couple of 195As, both on my todo list. I bought the first one for fun, but it had slowly wandering readings (i.e. a few 10s of counts over the course of a day). As a TEA sufferer, I naturally bought another one to compare it to... and found that it wandered even worse :palm:. Despite this, I still dont think that this is normal behaviour, just that they are suffering from the same affliction. To be fair, the casing of the second one had been smashed to bit so it wasn't in best of condition. Anyway, the point of this waffling is that the second one arrived with the uncal error, and a quick subsitution showed that the xicor X2212D NVRAM was at fault. A "new" chip from eBay solved the uncal problem (but not the wandering readings). BTW, at least on my units, the 5V regulator runs really hot. I'd be interested to know if your 195 is the same. --- End quote --- Was resolving your Uncal error accomplished by simply swapping the X2212 or was it more involved? Obviously you would need to run at least a partial calibration to get halfway sensible cal data stored. And, I presume, to get an OK checksum in the 2212. Wilko |
| Swainster:
I think saving anything to the NVRAM gets rid of the uncal message - I certainly haven't done any adjustment on it yet. Just to be clear, the uncal message is gone but as expected the original calibration data is still lost. I'm still looking for a suitable AC source before I can start doing any adjustments. |
| wkb:
--- Quote from: Swainster on September 23, 2022, 03:10:51 am ---I think saving anything to the NVRAM gets rid of the uncal message - I certainly haven't done any adjustment on it yet. Just to be clear, the uncal message is gone but as expected the original calibration data is still lost. I'm still looking for a suitable AC source before I can start doing any adjustments. --- End quote --- Yes, obviously the original cal data is gone forever. On my unit I cannot get rid of the Uncal message, tried to cal some DC ranges using my Hp3478A as a comparison DMM! so I assume the 2212 is a goner. OK.. anxiously awaiting the slowboat from China here.. |
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